Fluid pumps manufactured presently often have no protection against run dry events caused by e.g. blockage of the fluid being pumped or other events (such as a locked rotor) that could result in damage to the pumps if power to the pump is not turned off. Correspondingly, pumps manufactured presently often have no capability for detecting a run dry condition or other possible harmful condition. The few models that do have such protection use very simplistic protection mechanisms.
For example, U.S. Pat. No. 5,076,763 discloses a circuit that detects an undercurrent or overcurrent condition (caused by a run-dry condition or a blockage/locked rotor condition), and shuts off the power to the pump motor via a relay. However, the protection circuit there merely operates as a recycling timer. If the condition persists, the unit keeps cycling ON and OFF; however, if the condition does NOT go away, the pump will still destroy itself because it will continue to receive power (intermittently). The '763 patent discloses an undercurrent detector stage, which shuts off a pump motor when an undercurrent is detected caused by the pump beginning to run free due to exhaustion of liquid from the sump or bilge. There is also a teaching that the rest period between turning a pump off after sensing an undercurrent and turning it back on is dictated and controlled by the next prior pumping cycle history of the system. There is however no teaching of turning off the pump indefinitely in the case of reaching a predetermined number of attempts to turn the pump back on and sensing each time an undercurrent condition when turned back on. The protection circuit of the '763 patent can detect and protect against both blockage (increase in current) and loss of fluid (decrease in current). However, it is still merely a recycling timer, and so it will still allow the pump to be damaged by a constant “run dry” condition or blockage. Also, its design is also “pump specific” in that the levels of currents it detects are determined by the values of electronic components in its circuit design. For different pumps and motors, different values are required. Hence different PCB board assemblies and part numbers are required for different pumps. Still also, it also has no diagnostic capability: it gives no indication to the user whether the problem is run-dry, blockage, over temperature, circuit failure, sensor failure, or other condition. Further, it has no temperature sensing capability to protect against overheating; it cannot limit the number of times that a fault condition is allowed, then stop until commanded to reset; it cannot learn or adapt to its environment and change its operation accordingly (for example, adapt to a lower or higher input voltage, or adapt to changing operation parameters due to motor wear); it cannot store information about the pump, such as the serial number, manufacturing numbers, log hours of operation, number of failures, or other historical information of use in diagnosing problems with the pump or of use in preventing problems from occurring.
What is needed is a protection circuit that adapts to the (possibly) changing (e.g. gradually, over time) nominal operating values of the load it is protecting, and, further, is more than a simple recycling timer, turning off power in cased of a sensed abnormal operating condition (undercurrent or overcurrent), and then simply turning on (after a predetermined period) and off again and again as long as the underlying cause persists.
In addition, some loads use large amounts of electrical current. For example, battery-powered vehicle electrical systems carry large electrical currents to their loads (a starter motor, for example), and heavy and expensive copper wiring is required to carry such large electrical currents. The loads in a vehicle are typically controlled from centralized panels (such as a dashboard or equipment panel) and also from distributed locations about the vehicle (such as multiple switches for a water pump on a boat or RV). Using conventional electrical control system approaches, heavy wire must be pulled from the power source to the control switch or switches, and also to the load. The cost, size and weight of the wiring required is often objectionable, and voltage drops because of long wiring runs are characteristically problematic.
Thus, what is also needed is a way to avoid having to use heavy wire to connect the power source to the control switch or switches.